In the manufacture of microcircuit dies, chemical/mechanical polishing (CMP) is used to provide smooth topographies of the semiconductor wafers. One who is skilled in the art is familiar with such CMP process. Referring now to FIG. 1, illustrated is a sectional view of a conventional wafer carrier head assembly 100 comprising a carrier head 110, a carrier gimbal 120, a drive shaft 130, a wafer carrier 140, and a wafer retaining ring 150. Also shown in FIG. 1 is a conventional semiconductor wafer 160 mounted within the wafer carrier 140, and a polishing platen 170. A wafer polishing surface 165 and a platen surface 175 are also designated. Ideally, the wafer surface 165 and the platen surface 175 are parallel and exactly horizontal. However, the carrier gimbal 120 is designed to allow for local deviations from the horizontal between the wafer surface 165 and the platen surface 175. The gimbal 120 is effectively a universal joint, between the drive shaft 130 and the carrier head 110. Should there be a deviation of the platen surface 175 from the horizontal at any point, the gimbal 120 allows the carrier head 110 to follow the contour of the local surface by tilting appropriately on two orthogonal, essentially-horizontal axes 121, 122.
A major problem exists with the conventional gimbal design shown, i.e., the higher the gimbal is from the wafer surface 165, the slower is the response of the carrier head 110 to deviations from the horizontal. The fact that a relatively long moment arm 180 exists between the conventional gimbal 120 and the wafer surface 165 causes the problem. Therefore, efforts have been previously made to shorten the moment arm 180 in order to make the gimbal 120 more responsive. Ideally, the moment arm 180 would be minimized by placing the gimbal 120 in the carrier head 110, as close as physically possible to the wafer surface 165. Such a location would provide a gimbal with the fastest response to local deviations of the platen 175 from the horizontal. However, physical considerations make placing a mechanical gimbal 120 deep within the carrier head 110 extremely difficult.
Accordingly, what is needed in the art is a gimbal that can be mounted in the carrier head in close proximity to the semiconductor wafer to provide the most rapid response possible to local variations of the platen from the horizontal.